1. Field of the Invention
Apparatuses consistent with the present invention relate to an optical branching module that performs optical signal processing such as optical branching for an optical signal inputted by an optical cable on an input side, and outputs optical signals subjected to optical signal processing by optical cables on an output side, and particularly, to an optical splitter module that contains an optical splitter and to an optical connector boot.
2. Description of the Related Art
Optical Branching Module
In general, in an optical branching module, for example, cables on an input side and an output side are drawn out of a case. The cables drawn out of the optical branching module are fixed thereto so as not to cause a malfunction such as a joint failure even if pulling force is applied to the cables. FIG. 1 and FIG. 2 show a related fixing structure of the cables.
In FIG. 1 and FIG. 2, one end of each of a plurality of cables 500 is housed in a case 501, and other ends thereof are drawn out of the case 501. End portions of the cables 500 housed in the case 501 are subjected to step peeling. Such portions of the plurality of cables 500, which are subjected to the step peeling, are coated with a double-sided adhesive tape 502, with the cables in a state of being spaced from one another. The portions of the plurality of cables 500, which are coated with the double-sided adhesive tape 502, are placed between two columns of positioning pins 503 of the case 501, and a lower surface of the double-sided adhesive tape 502 is pasted onto the case 501. A region between the two columns of positioning pins 503 of the case 501 is covered with a protection cover 504 from the above, and an upper surface of the double-sided adhesive tape 502 is pasted onto the protection cover 504. The force for fixing the cables 500 in the case 501 is obtained by adhesive force of the double-sided tape 502.
In the related art optical branching module, the adhesive force of the double sided tape 502 is not sufficient with respect to magnitudes of various pulling forces applied to the cables 500. In particular, the adhesive force of the double-sided adhesive tape 502 deteriorates in an outdoor environment, and accordingly, the fixing force thereof decreases.
Optical Cable Boot
Onto a joint portion between an optical connector such as the optical branching module and optical fibers or between the optical branching module and optical cables, an optical cable boot for the optical connector (hereinafter referred to as an optical connector boot) is attached in order to reduce an optical transmission loss caused by side thrust increased when the optical fibers are curved.
A related optical connector boot is disclosed in Japanese Patent Laid-Open Publication No. H8-122567 (published in 1996). FIGS. 3A and 3B are schematic views showing an outline of the related optical connector boot: FIG. 3A shows a state where no load is applied to the optical connector boot; and FIG. 3B shows a state where a load is applied thereto downward toward the right in the drawing.
As shown in FIG. 3A, slits 335 are formed at a predetermined pitch P in an optical connector boot 301. With regard to the slits 335, two thereof which are perpendicular to a length direction of the optical connector boot 301 and open outward symmetrically with respect to each other make a pair, and a plurality of the pairs form the slits 335. Moreover, the slits 335 are formed at a constant width with respect to a depth direction when coupling portions 333 are taken as bottoms.
When each optical fiber (not shown) is coupled to a connector plug (not shown), and is fixed to a predetermined device, the optical fiber is curved downward owing to its own weight. In this case, the optical connector boot 301 is attached onto the joint portion, whereby a curvature radius of the curved optical fiber is increased, and the side thrust is reduced.
Then, when the optical connector boot 301 is attached onto the optical fibers (not shown), and is assembled to the connector plug (not shown), the optical connector boot 301 is gently curved downward as shown by dotted lines of FIG. 3B owing to the weight of the optical fibers.
In the related art optical connector boot, the width of the slits is constant with respect to the depth direction thereof. Accordingly, when a pulling load is applied to a direction (downward in FIG. 3) of 90 degrees with respect to a direction where the optical connector is attached/detached onto/from the optical fibers, the optical fibers are not curved into a shape shown by the dotted lines of FIG. 3B, but are positionally shifted therefrom in a shearing direction at the coupling portions 335 of the slits 335, the optical fibers are bent at an acute angle, and the side thrust is increased, resulting in a problem that the optical transmission loss is increased.
In the related optical branching module, the adhesive force of the double sided tape 502 is not sufficient with respect to magnitudes of various pulling forces applied to the cables 500. In particular, the adhesive force of the double-sided adhesive tape 502 is deteriorated in an outdoor environment, and accordingly, the fixing force thereof is decreased.